This invention relates to a process for the production of resilient, flexible polyurethane foams.
There are essentially two major groups of products which are of industrial significance as flexible and resilient cellular upholstery materials. These are, on the one hand, flexible and resilient polyurethanes and, on the other, latex foams. There are differences between the two product groups with regard to starting materials, production processes and mechanical properties and with regard to the use thereof Latex foams accordingly have a somewhat different compressive strength curve profile to DIN 53577 or ISO 3386, parts 1 and 2. Unlike polyurethane foams, latex foams do not exhibit a distinct plateau in compressive strength, but instead exhibit an almost linear increase in compressive strength within a defined compression range. This property is desirable or even necessary for certain applications. The average bulk density of latex foams is at least 60 kg/m.sup.3 or usually higher, and such foams exhibit compressive strengths of between 3 and 4.5 kPa. Such grades of foam are preferably used for the production of high quality mattresses.
Polyurethane foams normally exhibit higher compressive strengths within this bulk density range and furthermore a different compressive strength/compression profile.
It would be desirable to influence the compressive strength/compression profile of polyurethane foams in such a manner that behavior similar or identical to that of latex is achieved while retaining elevated resilience. These polyurethane foams should additionally exhibit low residual deformation and low moist ageing values. This is a particularly important criterion.
DE-A 19,508,079 describes a process for the production of resilient foams of low hardness which have very good mechanical properties in the lower bulk density range.
However, using the curing process specified therein, difficulties arise in achieving the required range of properties at higher bulk densities.
Accordingly, an object of the present invention was to provide a process for the production of highly resilient polyurethane foams having behavior similar or identical to that of latex, combined with good ageing behavior, particularly moist ageing behavior. This process should consistently yield polyurethane foams having this range of properties within a bulk density range from approx. 30 to 65 kg/m.sup.3.